The Humma field is located in the southwest corner of the Divided Zone (DZ) bordering Kuwait and Saudi Arabia. Marrat production was discovered in the field in 1998 and brought on-line in 1999.
The Jurassic Marrat formation consists of several distinct limestone layers of varying reservoir quality and productivity. These layers are generally classified as tight to low permeability limestones. Production from the Marrat formation is characterized by high initial production rates but with quick steep declines.
To maintain producing rates the wells were acidized on a frequent basis with 15% HCl acid. The benefit of these frequent acid treatments diminished over time as post-acid treatment production gains dropped. As a result, several stimulation alternatives to enhance the productivity were investigated.
This paper describes the development and application of a deep penetrating acid system in stimulating the Marrat limestone formation in the Humma field. Core samples and reservoir rock properties were used to customize the system. The understanding of reservoir rock properties, the systematic approach of treatment design, and sustained production results were key factors in employing this system.
The resulting deep penetration acid system was found to be favorable for acid penetration and uniform distribution over the long limestone pay intervals. The system was tailored to penetrate "deep" into the formation while removing near well bore damage. The system creates uneven etching patterns in the formation, connecting the well bore with undamaged native permeability of the carbonate reservoir.
The system was applied in three Humma Marrat wells. In all three cases excellent incremental production results were achieved. In the first well the production increased by 201% and sustained since 1 1/2 year to date. In the second well the incremental production was 151% and it was sustained for six months.
In the third well the expected initial production was 2,500 BOPD with ESP, but using the deep penetration acid technique the well started flowing by itself and sustained a production of 3,381 BOPD as Natural Flow since one year to date. The flowing bottomhole pressure is still significantly high, and as a result of this the well has just been completed with TG5600 pump and is producing 4,500 BOPD. This well is being monitored with the application of VSD and the production is expected to be +/- 6000 BOPD which will result in an incremental gain of 140% in comparison to the expected initial production rate.
The procedure and the placement techniques of using pinpoint injection packers, straddle packers and diverting systems, and the subsequent test results, provided insight into this treatment success and of limiting the uncertainties involved.
The post-job analysis allowed further optimization of these processes, which would facilitate similar applications in the future.
The Humma field is located in the southwest corner of the Divided Zone (DZ) bordering Kuwait and Saudi Arabia (Fig. 1).
To date, three wells have been drilled and completed in the Marrat reservoir. Well-A and Well-C, drilled on the crest of the main structure, are producing ±3,500 BOPD each of 35 degree API crude. Well-B drilled down dip, is producing ±1,000 BOPD with 27–29 degree API crude. Well-B was drilled between two faults, which is believed to be contributing to the lower API and productivity of the well.
The average reservoir depth is 9,585 ft, and average porosity and permeability is 12.2% and 1 md to 80 md respectively.
To enhance the productivity of the Marrat reservoir a matrix acid stimulation program was undertaken using Pin Point Injection (PPI) packer and a chemical diverting system.